The batteries have an average lifetime of approx. one year depending on the usage, e.g. less than a year if the Danalock is connected to a gateway.
You will receive warnings when the batteries are running low, and it is easy to buy new ones on the Danalock webshop or at a local Danalock retailer.
To change the batteries you gently click off the lid with a small flathead screwdriver, unscrew the two small philips-screws that hold the battery pin.